RF telemetry: strategies for locating tagged Pangolins

A directional Yagi antenna linked to a receiver tuned to the frequency of an animal's radio tag is commonly used for tracking (see previous post). However, the use of RF tracking for finding and following pangolins that have already been tagged faces several challenges and unknowns:

• Pangolins sleep in burrows most of the day and usually only emerge for a period of say 4-5 hours at dusk or at night
• Tracking through the bush at night is arduous and possibly dangerous with other game in the vicinity such as rhino, hyena, leopard or warthog, as at Mundulea
• The daily activity pattern, ie the time that a pangolin emerges above ground and returns to a burrow, varies from individual to individual, and probably depends on the season, weather or rain and local availability of prey.
• Pangolins are known to utilize several dens in a rather random fashion.
• It is speculated that Cape pangolins may possibly hibernate underground during the cold winter season (when ants may also hibernate).
• If pangolin is discovered asleep in its den, then the disturbances and especially scent left by the tracker will probably cause the pangolin to look for an alternative den for the following nights.
• When the animal is above ground, the ground-ground detection range of the Yagi apparatus may be 1-2km on the flat, but when below ground the range may only be a few 100's of metres, depending on how deep the burrow is and whether it is in rocky territory. So, despite the reduced distance the tracker can cover at night, the area that can potentially be surveyed for signals if the pangolin is above ground would then be more than 16x as large.
• A pangolin may not emerge from its den every night, some are rumoured to have stayed underground for several days. Therefore, a systematic search pattern at night assuming a detection range of several km's when a pangolin is active above ground may miss a pangolin still in its den, which would need a finer search pattern for the reduced detection range of only a few 100m.  
• Climbing any high point will increase the Yagi's detection range, for example a small mountain may provide a vantage point to detect signals and their rough bearing from 5-10km away. However, on descending the signal may be lost again, occluded by lower intervening hills or rocks. For triangulation onto the pangolin's location, a second high point is also needed that can be quickly reached, e.g. on the same night.
• The home range of a large pangolin is also likely to be large. Establishing first estimates of home ranges sizes vs. animal weight, age, local ecosystems and seasonal prey availability are important long-term goals for our project. Some studies in Zimbabwe and South Africa have been published, e.g.
     Martha E. Heath and the late I M Coulson, 'Home range size and distribution in a wild population of Cape pangolins,
     Manis temminckii, in North-West Zimbabwe', Afr. J. Ecol. 1997, Vol. 35, pp 94-109. but home ranges in other environments are unknown. 
• In one night a pangolin can cover several km, so the tracker that eliminates an area one day may have to start over again the next.
• Without a rough idea of the diameter of the particular pangolin's home range, it is very difficult to design an efficient search pattern. If the home range is 6km across, then the area to be searched is 9 times as large as when the home range is only 2km across.
• Even when the animal is active as it forages close to the ground, the RF signal can disappear for many seconds or more when the animal walks behind a rock. So, too rapid a scan with the Yagi antenna may miss the signal from a pangolin that is within range.
• Once a signal is detected, if it is a long way away and the tracker is on foot, then the pangolin may go to earth again after a few hours of foraging before the tracker catches up.
• When closing on a pangolin, if disturbed it can move faster through dense thorn bush (like a small tank) than the human tracker, until the tracker gets within a few 10's metres when it will stop and freeze.

It's clear that the search for a lost pangolin becomes a probability-based game, like hunting a needle in a haystack!

 

(photos by Emiel de Lange)

(Comments are invited here from any others experienced in pangolin tracking on the methods which they have found most efficacious.)

The following strategy, seen in hindsight after the October/November 2011 field work in Mundulea, may be effective:

1. Prepare an understanding in advance with any local neighbours to be permitted to track pangolins at night into their properties if that is likely.
2. First try to establish the pangolin's pattern of daily activity by climbing to the highest local viewpoint and waiting from dusk into the night, checking at regular intervals in different directions to discover the time that first signals are detected and of course a rough compass bearing of any signal is invaluable. An estimate of the time that the pangolin emerges above ground to forage will help fix the starting time for longer-range detection searches on subsequent nights.
3. If a signal is detected, try to get to a second vantage point as soon as possible to get a rough triangulation fix on the pangolin's location. (The ideal would be to have more than one tracker at different high points with Yagi's in radio or cellular communication) 
4. Use vehicles wherever there is a network of drivable tracks that are closer together than the expected above-ground detection range. This is a fast way of reducing the search space. Walking cannot cover enough search territory in one night, and the next night the animal may have moved several km, so the previous night's results may be out of date.
5. Trying to find a pangolin during the day time when it is down a burrow without a rough idea of its location within +/-2km is likely to be fruitless.
6. Once a signal is (re)detected, preferably after an approximate trangulation, try not to lose the signal at all costs, checking the bearing and strength regularly at any rises in the ground en route. Make sure radio or cellular communication with base is in place in case the vehicle has to be abandoned, there are any accidents or encounters with dangerous game.
7. Use a GPS unit to record the tracker's path and mark waypoints to make it easy to find the way back after walking in the bush at night.
8. Once the pangolin is discovered, e.g. sleeping down a den, do not lose it again that night, instead wait quietly from a distance downwind until it emerges (or follow it from a distance to establish its next den). Once one night passes, especially if disturbed by the tracker's scent or noise, the animal may move to a new den beyond the RF detection range from the previous den.